The present invention relates to an office call state display system for displaying the call state of each extension telephone number (extension telephone) on a switch board installed in a company or the like and, more particularly, to an office call state display system for displaying the call states of extension telephone numbers in branch offices connected to other exchanges by using the common channel signaling system No. 7 (complying with the CCITT) and executing a communication protocol based on the transaction capabilities application part (TCAP).
In a company using many telephone lines, a switch board (telephone exchange) including private branch exchanges is used to manually connect an incoming call of a representative telephone number to an extension telephone number (extension telephone). In addition, termination settings are switched by using a representative telephone number or dial-in operation. In addition, the telephone exchange performs processing of automatically connecting an incoming call of a representative extension telephone number to an extension telephone number (second number), i.e., automatic connection control, and outputs a speech announcement to request the input of an extension telephone number to a destination.
Such a telephone exchange is connected to a telephone network using an ISDN (Integrated Service Digital Network) to which the common channel signaling system No. 7 is applied. The telephone network based on the common channel signaling system No. 7 includes known signal transfer points and signal end offices. These signal transfer points and signal end offices include subscriber exchanges accommodating data communication units and telephones, relay exchanges for performing exchange among many subscriber exchanges, and the like. The subscriber exchanges and the relay exchanges execute programs for processing execution management, call processing, maintenance/operation, and fault processing based on the stored program control (SPC) scheme.
In general, a control unit (computer) is connected to the relay exchange. This control unit controls the overall telephone network to intensively manage, for example, fault data and execute the communication protocol (the general-purpose protocol for retrieval, registration, and change of control data, registration of the positions of terminals in mobile communication, registration of information between exchange maintenance/operation management centers, and data transfer for access operation between an exchange and a network database in information read operation or the like) based on the transaction capabilities application part (TCAP). The subscriber exchanges and the relay exchanges comprise exchanges and signal control units. The exchanges are connected to each other through trunk lines based on the inter-office signaling system, and the signal control units are connected to each other through a common line.
Each exchange performs relay control as well as subscriber control and communication channel switching. Each signal control unit sends inter-office signals to execute programs for processing execution management, call processing, maintenance/operation, and fault processing based on the stored program control scheme. The telephone exchange connected to such a telephone network displays call states such as the busy and idle states of the connected subscriber terminals (telephones and data communication units).
Display of such call states is executed by each signal control unit, which stores extension telephone numbers (second numbers) input upon termination of representative extension telephone numbers in the main memory or the like, according to the following control sequence.
First of all, the telephone exchange periodically (e.g., 6-sec intervals) transmits a call state display request signal including extension telephone number group information to the subscriber exchange that accommodates the telephone exchange. The subscriber exchange reads out call states corresponding to the telephone number group of the extension telephones connected to the telephone exchange from the main memory, and returns this call state display response information to the telephone exchange. The telephone exchange displays the call state of each extension telephone number by blinking the corresponding lamp or on a cathode-ray tube (CRT) or the like on the basis of the returned call state display response information, thereby displaying the call state of each extension telephone.
xe2x80x9cRepresentative Selection Systemxe2x80x9d disclosed in Japanese Patent Laid-Open No. 8-23378 is an proposal associated with display of such call states. In this prior art, upon termination to a representative telephone number, the extension telephone numbers and user names of the extension telephones belonging to this representative telephone number are displayed on the screen of each extension telephone. This prevents a specific extension telephone from responding to an incoming call to an unspecified number of extension telephones.
In the above prior art, the telephone exchange installed in a head office cannot display the call states of extension telephone numbers in a branch office or the like which is connected to another exchange and belongs to the same corporated body. The users in the head office cannot therefore know the call states of the extension telephone numbers in the branch office.
In addition, when the telephone exchange installed in the head office executes a control sequence to display the call state of connected extension telephones (extension telephone numbers), the loads of processing on the telephone exchange and subscriber exchanges are heavy.
It is an object of the present invention to provide an office call state display system which allows a grouped second telephone exchange to monitor the call states of extension telephone numbers in a first telephone exchange.
It is another object of the present invention to provide an office call state display system which can transmit a display signal representing the call state of an extension telephone number whose call state has changed (busy, idle, or unmounted state) and reduce the load on telephone exchanges and subscriber exchanges.
In order to achieve the above objects, according to the present invention, there is provided an office call state display system comprising a telephone exchange to which at least one first subscriber terminal is connected, a first subscriber exchange to which the telephone exchange is connected, a second subscriber exchange to which a plurality of second subscriber terminals to which extension telephone numbers designated by a common representative extension telephone number and an extension telephone number group are assigned are connected, and display means, connected to the telephone exchange, for displaying a call state of the first subscriber terminal and call states indicating busy, idle, and unmounted states of the extension telephone numbers assigned to the second subscriber terminals, the telephone exchange comprising first control means for sending, through the first subscriber terminal, a call state request signal including the representative extension telephone number and extension telephone number group information of the second subscriber terminal whose call state is to be known, and controlling the display means on the basis of the call state information from the second subscriber exchange, and the second subscriber exchange comprising second control means for returning call state information indicating a call state of each of the second subscriber terminals to the telephone exchange through the first subscriber exchange in response to the call state request signal from the telephone exchange.